The molecular mass of acid phosphatase (APase) from Solanum tuberosum is estimated as 111 kDa using denaturing SDS-PAGE. The prime catalytic di-iron Fe²⁺/Fe³⁺ site (1.62 ± 0.2 mole) together with the co-catalytic sites of manganese, zinc and trace copper (0.397 ± 0.135 mole) in the enzyme have been determined by the GF-AAS technique. The quantitation of the biphasic release of iron species from the enzyme has been carried out spectrophotometrically. The reduction
(~70-72%) in biological activity of APase after removal of the divalent metal constellation of co-catalytic site made up of Fe²⁺, Mn²⁺, Cu²⁺ and Zn²⁺ is established after duplicate treatment of enzyme from a Chelex-100 column. The significance of redox active Fe²⁺/Fe³⁺ metal cofactors at the active site of the enzyme correlates well with the affinity of substrate binding towards the di-iron site in terms of kinetic parameters. A physiological defense activity of APase is established in terms of its quantitative pUC-19 plasmid DNA cleavage activity.

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